A patent, somewhat related to the present invention, is U.S. Pat. No. 4,132,048, which was issued to T. T. Day on Jan. 2, 1979. In the Day patent, which is owned by W. R. Grace & Co., the assignee of the present invention, the bag inside the chamber and the chamber are both evacuated to a relatively low reduced pressure, at which time the bag is sealed inside the chamber. Continued evacuation of the air in the chamber outside the bag caused the bag to balloon out due to residual air pressure therein, at which time it is heated by heaters on the inside of the chamber. The chamber is then vented in a controlled manner to aid in controlling the heat caused shrinkage of the bag onto the food product.
The Day apparatus and process operates well, but the present invention offers distinctions and additional advantages. Among these advantages are that the shrinking of the bag is controlled better. For example, as the bag is heated to a temperature at which the plastic of the bag material begins shrinking, the bag will commence shrinking regardless of whether or not that is the most opportune time with respect to the degree of evacuation of the surrounding chamber. In the present invention, the diaphragms control the start of shrinkage of the bag, and they are fully controllable.
Both the present invention and the apparatus of the above mentioned Day patent overcome numerous problems present in the prior art of hot water systems. It has been heretofore known to use pre-formed packaging such as bags for relatively large meat products such as whole rounds of beef or whole pork loins, but the art heretofore has been to shrink these bags using hot water. There are many disadvantages with hot water systems, including very poor utilization of the energy in the hot water (it has been estimated that as low as 3% of the heat energy in the water goes into the useful work of bag shrinkage, and the rest is wasted). In addition, handling of the hot water itself is a great problem since the work is done in meat packing cold rooms. These cold rooms consume enormous amounts of energy to keep them refrigerated and thus floor space is very valuable. The present invention is to a dry process, which saves all of the sloppiness and mess and safety hazards associated with water getting on the floor, and in addition it utilizes much less valuable floor space than is utilized by hot water systems.
An important advantage of the present invention resides in the provision of flexible diaphragms inside the heated platens inside the vacuum chamber. These diaphragms accomodate many difference sizes and shapes of goods, and deliver heat to all of them, as needed. The platens heat the diaphragms and the diaphragms deliver that heat to the heat shrinkable bag, and only to the bag by contact, which automatically accomodates difference sizes and shapes of products.
The invention also operates on a shorter time cycle because it does not need as low a vacuum pressure as some prior art systems, and that achieves important advantages over the prior art.
Another advantage of the present invention's flexible heated diaphragms is that difference sizes and shapes of food products or other goods can be accommodated in one machine with no changes to the machine. In the real world of food packaging, it is unlikely that a plant which packages large cuts of beef would also package processed meat products such as salami or balogna. However, there are many different sizes and shapes of large cuts of beef and there are many different sizes of salami shaped products. Thus, the invention's heated flexble diaphragms produce important advantages over the prior art in general.
Another advantage of the invention is that when necessary a rack can be utilized in the chamber between the lower heated diaphragm and the meat product with the bag resting thereon. By controlling the size and the spacing of the wires or other material making up the rack, the amount of heat imparted to the product by the heated diaphragms can be controlled. This is important with certain products, such as certain cheeses and certain processed foods, wherein more than a predetermined small amount of heat would be unacceptable.
Another advantageous feature of the invention resides in an optional closing bar, which further improves the operation of the invention method by causing the bag to balloon out towards the diaphragms before the diaphragms contact the bag, to thus improve the shrink and the quality of the final package.